1. Field of the Invention
The present invention relates to a welding wire-guiding tip, which hereinafter may be called as a welding tip for automatic arc welding equipment. Specifically, it relates to the structure of a wire guide hole opened to the tip described above.
2. Description of the Related Art
A wire to be used as a conventional electrode for gas metal arc (abbreviated as GMA thereafter) welding, and a filler wire to be used in non-consumable electrode arc welding such as tungsten inert gas arc (abbreviated as TIG thereafter) welding, have round shapes in cross section, and a guide hole of the welding tip for guiding the wire to weld portion has each round shape in cross section.
FIG. 10 is a sectional view showing a current contact tip for the GMA welding and its guide hole 2 both of which have been known in the prior art. Usually, the length L of a tip 1 is about 40 mm, and a stepwise round guide hole 2 whose diameter is larger on the side of a tip inlet portion 3 and smaller on the side of a tip outlet portion 4 is provided at the center portion in its radial direction. The diameter D of a large diameter portion is set to a larger value than the diameter of the wire described above by about 1 mm, and the diameter d of a small diameter portion is set to a larger value than the diameter of the wire described above by 0.2-0.4 mm, for example, in the case that the diameter of a wire passing through it is about 1.2 mm. Chromium-copper or beryllium copper are normally used as the material of the tip 1 for welding to the wire for GMA from the view points of abrasion resistance and current contact. The wire is supplied from the side of the tip inlet portion 3 in a more or less bent condition so that the current contact may be firmly carried out at the tip outlet portion 4.
FIG. 11 is a sectional view showing a tip outlet 4 and illustrates such a condition that a wire 5 passes through the guide hole 2 of the tip 1. The current contact is carried out in the form that the wire 5 having a round shape in cross section may be brought into contact with the inside of the guide hole 2 having a circular shape in cross section at one point between a line and a point.
This welding tip 1 is mounted on an unillustrated welding torch, which is used in semiautomatic welding or loaded on a welding robot. In the case that the welding torch 1 is loaded on the welding robot, the wire 5 is usually taken out of the tip 1 while the condition at the time of welding is assumed, the welding route is stored by tracing the welding groove at the tip of the wire 5, and then, the welding is carried out by play backing. In the process for tracing the welding groove, however, as the contact pressure by the welding groove is applied on the wire 5, the contact point between the guide hole 2 and the wire 5 is varied. Then, the position at the wire tip at the time of playing back during welding and the initial position at the wire tip may be varied sometimes. It is easy for the tip of the wire 5 come out of a target position during welding, and the beads are zigzagged.
Therefore, in order to reduce such an inconvenience, it is desirable that the wire 5 come out in a straight condition as much as possible and from the guide hole 2 having less clearance. However, as some clearance is necessary in order to feed the wire 5 smoothly, and if the straight wire 5 is arranged as to pass through a straight guide hole, the contacting energized position between the guide hole 2 and the wire 5 cannot be fixed and stable welding work becomes difficult. Therefore, when such a straight wire is adapted, there is an example disclosing a device for pushing a wire to an energized tip hole surface horizontally by means of a spring (Japanese Patent Application Laid-Open No. 64-18582).
Incidentally, the wire 5 fed to the welding tip 1 is not always clean, but it is sometimes attached with rust on its surface, chips produced by the contact between the wire and the internal surface of the conduit or the tip 1, and the released matter produced at the time of passing the feed roller in a wire feeding apparatus. The surfaces of mild steel wires are protected by copper plating for rust inhibiting. In this case, it is sometimes attached with the released matter from metal plating in addition to the foreign matter described above. This foreign matter is brought to the welding and tip 1 along with the wire 5 and plugged between the guide hole 2 and the wire 5, resulting in preventing the smooth supply of the wire 5 or a current contact to the wire 5. As a result, in the case of GMA welding, erratic arc is generated frequently and there are some problems such as frequent spatter generation and arc instability. There were some cases that the tips and the wires have been frozen to each other by the spark between them at the beginning of welding.
Since the problems described above easily occur as a guide hole diameter is made smaller and close to a wire diameter, the guide hole diameter is usually set larger than the wire diameter by approximately 0.2-0.4 mm.
Incidentally, for extracting foreign matter smoothly, Japanese Utility Model Application Laid-Open No. 56-142880 proposed a structure as shown in FIG. 12. A space 40 is arranged on the way to the guide hole 2 and a horizontal hole 6 passes through an energizing tip 18 from the space 40 to an outer surface thereof to release the foreign matter from it. Even by means of this method, however, the plugging-up of the foreign matter still occurs when the hole diameter at the tip of the current contact tip is made smaller than that of a usual value, and the guide hole diameter itself is still its usual value without any change. Therefore, there has been no improvement in the rattle of the wire 5 within the guide hole 2.
With reference to the ceramic guide tips used in hot wire TIG welding, the detailed description will be given in the following. In the hot wire TIG welding, some insulating tips of a ceramic matter for a filler wire guide are often disposed after the wire passes the current contact tip in order to make an extension portion for causing heat by energizing the filler wire long and to make the fluctuation of the tip of the wire less.
FIG. 13 is a sectional view showing a structure of the tip portion of a TIG torch previously proposed by the present inventors (disclosed in Japanese Patent Application Laid-Open No. 3-297574). This torch 16 is arranged so that a filler wire 5 may be fed in parallel with and close proximity to a tungsten electrode 9. As a result, the circumference of the torch can be made small and the execution of welding in a narrower space become easy. This has such an effect of enhancing the tolerance in arc length and remarkably improves the practicability of a TIG welding robot. In addition, such a hot wire method by energizing the wire 5 for increasing the quantity of wire deposition is adapted.
In FIG. 13, an insulating guide tip 10 for supplying the filler wire 5 and the tungsten electrode 9 are each held by an exchangeable mechanism, e.g., a screw stopper, to a load tip 8 mounted on the edge of a hollow torch body 7. In addition, a shield nozzle 11 produced by ceramics is inserted into the outer circumference of the edge of the torch body 7. Further, there is a passage (unillustrated) for argon as a shield gas in the inside of the torch body 7 so as to be blown out into the inner circumference of the edge of a nozzle 11. Water cooling pipes (unillustrated) having a conductive double tubular structure made of copper are provided to the inside of the hollow torch body 7, and the tip of the outer water cooling copper pipe is connected to the load tip 8. Therefore, the water cooling copper pipe cools the load tip 8 with cooling water and at the same time, an arc 13 can be generated between the tungsten electrode and a base metal 12 by energizing the load tip 8 and the tungsten electrode 9. A wire guide tube 14 is disposed in the axial direction of the nozzle 11 in the inside of the torch body 7, and a load tip 15 for use of wire is placed at the lower tip of it. The wire 5 reaches a base metal by passing through the current contact tip 15 and the wire insulating guide chip 10.
In the TIG torch 16 of FIG. 13, it is desirable to supply the wire 5 to just under the arc 13 as much as possible in order to make it easy to operate the TIG torch. On the contrary, while automatic welding is carried out, the wire 5 is detached from a base metal 12 due to a certain reason and a globule is often formed at an edge thereof. In such a case, the globule is brought into contact with the tungsten electrode 9 and the arc 13 is disturbed, resulting in inability of welding work, if the tungsten electrode 9 and the wire 5 come in too close proximity to each other. In order to prevent this, it is preferable to make the gaps in surfaces between the tungsten electrode 9 and the wire 8 wider to some extent.
In the case that there is no clearance between the wire 5 and the guide hole 17 and that the wire 5 is straight, the gap between the tungsten electrode 9 and the wire 5 may be at shortest 0.5 mm or more and more preferably approximately 1 mm. However, since a wire guide hole 17 in the insulating guide chip 10 had its round shape in cross section of 1.4 mm in diameter corresponding to the wire of 1.2 mm in diameter, there were some cases that the globules were brought into contact with the tungsten electrode 9 unless the gap actually had to be apart from each other by 1.5 mm or more in an average setting condition, because of the rattle between the wire 5 and the guide hole 17 and non-uniformity in curving tendencies of the wire 5. Then, there was such a problem that there was a great difference in arc heat between when the wire 5 was at the remotest apart and when it was in the closest proximity to the tungsten electrode 9, and accordingly, it was difficult to control the fusion condition of the wire.
From such reasonings, it has been desired to diminish the rattle between the wire 5 and the guide hole 17 by making the diameter of the guide hole 17 in the insulating tip 10 for guiding the wire 5 to be as small as possible so as to keep the distance between the wire 5 and the tungsten electrode 9 constant. When the diameter of the guide hole 17 was set 1.3 mm more or less corresponding to the wire 5 of 1.2 mm in diameter, there were some disadvantages in that the guide hole 2 was plugged up by foreign matter such as chips from copper plating, resulting in the inability to feed the wire, the wire 5 was chipped at the entrance of the guide tip 10, and the resulting chips were trapped by the side of the torch body 7. Further, the contact tip 15 and the tungsten electrode 9 were shortened with respect to each other to generate an arc within the torch body 7, resulting in damaging the torch 16. Accordingly, it was necessary to make the diameter of the guide hole 17 1.4 mm or more and clean periodically the torch body 7 so that no foreign matter 19 might be trapped thereby.
In the prior art described above, there is a disadvantage in that the tip position of the wire 5 broadly fluctuates in accordance with the supply of the wire due to the large gap between the wire 5 and the guide hole 2. Further, there still remains a fundamentally unresolved problem that in such a method as extracting any foreign matter from the horizontal hole 6 provided to the tip 1, the resulting tip structures are complicated, the tips become expensive and the plugging-up of the tips due to the invasion of the foreign matter is generated.
In the method of inserting round wire in cross section into the energizing tip having a round guide hole in cross section, however, there was a disadvantage in that continuous energizing can hardly be maintained and the arc off on the basis of momentary bad energizing is easily generated since the wire 5 and the internal surface of the guide hole 2 are brought into contact with each other on the contact between a line and a point. Since a large current flows at one point, there is such a risk that there may be a spark between the wire and the tip in the case of energizing start under the plugged condition between the wire and the tip and the wire may be fused into the tip, resulting in the inability of feeding the wire.